The aging and split aging characteristics of ternary aluminium-zinc-magnesium alloy with zinc contents of 3, 4.5, 6 and 7%, and magnesium contents of 1, 2 and 3% were investigated. Aging curves are determined as a function of tensile properties at the room temperature, 90°, 120° and 150°C.
In determination of split aging characteristics, the first stage aging was done in the room temperature with practical point of view and the second stage aging at 90°, 120° and 150°C was followed.
Conclusion are as follows:
1) In ternary Al-Zn-Mg alloys, increasing Zn amount accelereted the rate of age hardening and increase of Mg increases the strength of matrix. The strength of alloys increase with the amount of (Zn+Mg), but Mg has stronger effect than Zn.
2) Tensile strength of Al-Zn-Mg alloys aged at 120°C, do not differ from that of the alloys aged at 90°C, but yield strength showed maximun value at 120°C. In the range of low Zn+Mg%, the difference of aging temperature of 90° and 120°C has little influence on the value of tensile and yield strength, but tensile properties are generally low at the aging temperature of 150°C.
3) The Al-Zn-Mg alloy has remarkable split aging effect and from the practical point of view, the room temperature aging is necessary before the artificial aging. This split aging effect relates closely to the composition and the second stage aging temperature.
4) The influence of Mn and Cr on aging and split aging characteristics are almost negrigible.

抄録全体を表示

With the object to obtain sound AC8A aluminium alloy piston, the rate of solidification of this alloy was computed with method of electrical analogy and cleared up the relationship between solidification rate and casting conditions. The summarized results are as follows:
1) For analog calculation, an electrical model circuit were set up with oil condensers and carbon resisters. The computed results were nearly in coincidence with the experimental values in practical range of accuracy.
2) As to the casting condition, varying the thickness of the mold and casting, also temperature of the mould and pouring temperature, the effects of those aboves to solidifying velosity were measured.
3) Owing to the pouring disturbance of molten metal, it was found that the mold near the runner was overheated, and the solidification rate was exceedingly retarded. To prevent this retardation, the most simple and effective means is to be considered water cooling around the runner.
4) On the calculation of solidification rate of the piston pin boss, it was found that the core of piston pin, with the same reason described in item (3), reaches to high temperature owing to less heat capasity of that place at the end of pouring. This reduces the solidification rate and causes the development of typical micro-shrinkage-porosity on a inner surface of the piston-pin boss. The solidification rate and soundness of piston-pin boss shall be improved by applying water cooling in the core of piston-pin boss.

抄録全体を表示

Lo-ex is widely used because of its superior heat resistivity and particularly its low coefficient of thermal expansion, and it is standardized in our country as well as in various foreign.
This alloy is the Al-Si-Cu-Mg-Ni quinary system. As it has a considerably large content of Si compared with Cu, Mg and Ni, it may be considered Silumin added with Cu, Mg and Ni. From this point of view, Si percentage of 11.0-13.0 established in the above mentioned standards causes the contradiction to admit different structures in the primary crystal of the alloy belonging to the same specification, because the above range of Si content spreads over both sides of the Al-Si binary eutectic point.
The author and his associates have found the hyper-eutectic structure with the casting surface similar to the tortoise shell in one case, and the hypo-eutectic with the casting surface similar to the bullfrog's skin in other case, although the tested alloy is not tried for modification treatment with Na and even is fixed at the value of the hyper-eutectic side of the Al-Si binary system in Si percentage (ex. 12.0%). Clearing the cause for the aspect of both structures has developed into establishing the method of manufacturing Lo-ex with both structures.
A comparison, in addition, has been made on Lo-ex of both structures concerning the mechanical properties, the coefficient of thermal expansion and the castabilities.
The results obtained are as follows:
1) The adding elements of Lo-ex which have been certified to effect the transition of Al-Si binary eutectic point-Cu, Mg and Ni-have naturally same effect to the structure of this alloy. But, as far as Si percentage is maintained at 12% approximately and the content of Cu, Mg and Ni is within its specified range respectively, the different structures discribed above result from Ca contained in metallic silicon.
2) Lo-ex of Ca content less than 0.0050% produces hyper-eutectic type while Lo-ex of more than that produces hypo-eutectic.
3) The Na addition well-known as modification treatment certainly produces Lo-ex of hypo-eutectic type, but the casting surface does not assume bullfrog's skin. Moreover the raw materials used in this study are the virgin ingots only, and those Na contents are too small to have capability of modification treatment.
4) Lo-ex of hyper-eutectic type is superior in tensile properties, which is attributable to the far much less microshrinkage. The other mechanical properties have not any appreciable differences.
5) Lo-ex of hyper-eutectic type has the less coefficient of thermal expansion than that of hyper-eutectic type.
6) Lo-ex of hyper-eutectic type. has larger micro-shrinkage, and it is to some extent superior in runnability.

抄録全体を表示

Ignition temperature of magnesium alloys containing beryllium was measured in air and in dry oxygen, and discussed with relation to the results that beryllium addition on magnesium alloys provides with a protective film by oxidation.
There was found that beryllium addition increases ignition temperature only for the magnesium alloy containing 8% aluminium.
Presumably the ignition temperature of the magnesium alloy containing beryllium shall be influenced by properties and conditions of oxide film formed on metal surface.

抄録全体を表示

This report relates to electric discharge drilling machinability of titanium and its alloys. The specimens consist of titanium plate (Vickers hardness Hv=200) and Ti-8% Mn alloy (Hv=377) plate, and for comparison purpose with other metal, the plate specimen of mild steel (Hv=125), brass (Hv=117) and 2S (Hv=46) were selected.
As to the electric discharge drilling system, RC circuit (so called "Lazarenko-circuit") with DC and oscillating electrode were adopted. Kerosene, machine oil, light oil and water were used as machining solution.
The operating current was changed in five stages in the range of 0.5 to 4.5 amperes, and 0.8mmφ brass wire was used mainly for the electrode.
The results are summarized as follows:
1) Titanium and its alloys have extremly higher hardness than mild steel, but their electric discharge machinability expressed with drilling time, min/mm, was better than that of mild steel.
2) The drilling time varies with the operating current, but there exists minimum drilling time relating to some suitable operating current and in this experiment, that was about 2.5 amperes.
3) The drilling time is also depends on machining solution and, in this case, good result was obtained with machine oil.

抄録全体を表示